Trace Elemental Geochemistry and Depositional Environment of Shale Oil Reservoir Rocks within the Permian Lucaogou Formation, Jimusaer Sag

Abstract

By analyzing the geochemical indicators of trace elements and rare earth elements in shale oil cores, this paper clarifies the depositional environment of the Lucaogou Formation, and it provides some guidance for the exploration and deployment of shale oil in the Jimsar Sag. The average value of Th/U in the Lucaogou Formation is 1.89, which of V/(V+Ni) is 0.74, which of V/Cr is 3.05, which of V/Sc is 8.31, and w(Ni) are less than 40×10-6, indicating the terrestrial reduced environment. The Sr/Ba ratio changes frequently, ranging from 0.55 to 25.62, averaging 4.42, reflecting a higher paleo-salinity.87Sr/86Sr ratio ranges from 0.705286 to 0.705784, averaging 0.705486, and it is substantially lower than the average value of the strontium isotope of the crustaceous silicon-aluminum rock. Besides, 143Nd/144Nd ratio ranges from 0.512419 to 0.512722, and sediments have the characteristics of the origin of the mantle, reflecting the intracontinental rift formation environment. The analysis of rare earth elements indicates that the sediments has the characteristics of LREE relative enrichment, Ce weak positive anomaly and Eu negative anomaly, and furtherly excluded the possibility of marine sedimentary environment. Comprehensive analysis shows the sedimentary period of the Lucaogou Formation is a reduced and salty intracontinental rift lacustrine environment.